1. Field of the Invention
This invention relates to a variable capacity vane compressor having a construction which Is capable of changing the capacity or delivery quantity of the compressor.
2. Description of the Prior Art
A conventional variable capacity vane compressor includes a cylinder block, a rotor rotatably received in the cylinder block, a plurality of vanes each of which is radially slidably fitted in an axial vane slit formed in the rotor, two side blocks secured to opposite end faces of the cylinder block, respectively, a rotary plate received in a recess formed in one of the side blocks, in a manner rotatable between a partially operating position for minimizing delivery quantity of the compressor and a fully operating position for maximizing the delivery quantity of the same, and a piston which causes rotation of the rotary plate (Japanese Laid-Open Patent Publication (Kokai) No. 7-247982).
FIG. 1 is a longitudinal cross-sectional view showing the piston within the conventional compressor.
The piston 132 is slidably received in a cylinder bore 105c, for causing rotation of the rotary plate, not shown, via a link pin 131 fixed to the rotary plate.
The link pin 131, which is protruded toward a rear side of the compressor, has an end thereof partially fitted in an annular groove 132a formed in a peripheral surface of the piston 132, and partially fitted in an arcuate guide groove, not shown, formed in the rear side block 105, in a manner slidable along the guide groove. As the piston 132 reciprocates within the cylinder bore 105c, the end of the link pin 131 slides along the arcuate guide groove to cause rotation of the rotary plate.
A spring guide member 133 having a rod-shaped spring guide portion 133a is inserted into one end portion of the cylinder bore 105c. One end of the cylinder bore 105c is closed tightly by a spring seat 133b of the spring guide member 133 and an O ring 134. The spring seat 133b is fixed to the rear side block 105 by a pin 135. On the other hand, another end of the cylinder bore 105c is closed tightly by a plug 136 and an O ring 137. The plug 136 is fixed to the rear side block 105 by a pin 138.
The piston 132 has one end thereof formed with a low-pressure chamber 139 into which suction pressure Ps within a suction chamber is introduced. Another end of the piston 132 and the plug 136 define a high-pressure chamber 140 into which control pressure Pc (Pc.gtoreq.Ps) is introduced. The piston 132 is urged toward the partially operating position (leftward as viewed in FIG. 1) for minimizing the delivery quantity of the compressor, by a spring 141 interposed between a bottom surface of a bore 139a formed in the piston 132 and the spring seat 133b of the spring guide member 133 and the suction pressure Ps within the low-pressure chamber 139. At the same time, the piston 132 is urged by the control pressure Pc within the high-pressure chamber 140 toward the fully operating position (rightward as viewed in FIG. 1) for maximizing the delivery quantity of the compressor. Therefore, the piston 132 reciprocates within the cylinder bore 105c according to changes in the control pressure Pc. More specifically, when the control pressure PC becomes larger than the urging force of the suction pressure Ps and the spring 141, the piston 132 shifts toward the fully operating position, while when the control pressure Pc becomes smaller than the urging force, the piston 132 shifts toward the partially operating position.
At the start of the compressor, when the control pressure Pc is low and equal to the suction pressure Ps, the piston 132 is in its partially operating position as shown in FIG. 1, so that the rotary plate is also on a partially operating position side, whereby the compressor is operated in the minimum delivery quantity condition.
When the suction pressure Ps becomes higher than a predetermined value, a pressure control valve device, not shown, operates to increase the control pressure Pc within the high-pressure chamber 140, whereby the piston 132 is shifted from its partially operating position toward its fully operating position (rightward as viewed in FIG. 1). Force produced by this linear movement of the piston 132 is transmitted to the rotary plate via the link pin 131 for rotation of the rotary plate from the partially operating position side toward the fully operating position side, whereby the delivery quantity of the compressor is increased.
On the other hand, when the suction pressure Ps becomes lower than the predetermined value, the pressure control valve device operates to decrease the control pressure Pc within the high-pressure chamber 140, whereby the piston 132 is shifted from the fully operating position to the partially operating position (leftward as viewed in FIG. 1). This linear movement of the piston 132 causes the rotary plate to rotate from its fully operating position side toward its partially operating position side, whereby the delivery quantity of the compressor is decreased.
As described above, the delivery quantity of the compressor is continuously and variably controlled by rotation of the rotary plate.
However, in the vane compressor in which compressed refrigerant gas is used to reliably or positively project out each vane, if the compressor is started when the capacity or delivery quantity thereof is small, refrigerant gas cannot be compressed sufficiently, which results in degraded startability of the compressor.
To eliminate such inconvenience, a method has been proposed in which the minimum delivery quantity of a compressor is increased so as to ensure reliable projection of each vane and thereby enhance the startability of the compressor.
In this method, however, since the range of variable capacity of the compressor is reduced due to the increase of the minimum delivery quantity of the same, the compressor is not capable of reducing the delivery quantity thereof to a sufficiently low level as in the case of the proposed variable capacity vane compressor described above. As a result, it is required to switch the compressor on and off frequently.
To overcome this problem, another method has been proposed in which a main spring (stiffer spring) is provided on one side of the piston, for urging the piston toward the partially operating position thereof, while an auxiliary spring (softer spring) is provided on the other side of the piston, for urging the piston toward the fully operating position thereof, so as to make it possible to start the compressor by the use of difference in urging force between the two springs even when the delivery quantity of the compressor is small, thereby ensuring reliable projection of each vane and enhancing the startability of the compressor. According to this method, the compressor can have a wide range of variable capacity during operation thereof, so that the delivery quantity of the compressor can be decreased to the same level as in the proposed variable capacity vane compressor.
However, it is not a balance between the two springs that makes the minimum delivery quantity during operation of a compressor smaller than delivery quantity at the start of the compressor. Actually, the minimum delivery quantity becomes smaller due to drag of the rotor which acts on the rotary plate to limit the movement of the same.
Therefore, this method is not capable of reliably increasing delivery quantity at the start of the compressor, and reducing the minimum delivery quantity during operation of the same.